Mogrosides are a family of triterpene glycosides isolated from fruits of Siraitia grosvenorii (Swingle), also known as Momordica grosvenori (Swingle). Extracts of the fruits are commercially used as natural sweeteners. Four major compounds, Mogroside V, Mogroside IV, Siamenoside I, and 11-Oxomogroside V, have been identified from the fruits of Siraitia grosvenorii (Swingle) that are responsible for the sweetness of the fruits. See FIG. 1. Mogroside V is the most abundant of these four compounds at approximately 0.57% (w/w) of the dry fruit, followed by Mogroside IV and Siamenoside I, each of which contain four glucose moieties. 11-Oxomogroside V has a ketone group instead of a hydroxyl at C-11. See, e.g., Takemoto, et al., Yakugaku Zasshi, 103, 1151-1154; 1155-1166; 1167-1173, (1983); Kasai, et al., Agric. Biol. Chem. 53, 3347-3349 (1989); Matsumoto, Chem. Pharm. Bull. 38, 2030-2032 (1990); and Prakash, et al., J. Carbohydrate Chem. 30, 16-26 (2011).
All mogrosides share the same triterpene core, named mogrol. The aglycone mogrol is glycosylated with different numbers of glucose moieties to form various mogroside compounds. Mogroside is thought to be synthesized in the following manner: synthesis of cucurbitadienol from the common triterpene precursor squalene; P450 oxidations of cucurbitadienol to produce the aglycone mogrol; and glycosylation of mogrol to add the five glucoses one after another to produce mogroside V. See, Tang, et al., BMC Genomics, 12, 343 (2011). Both intermediates cucurbitadienol and mogrol exist in the fruit as they have been isolated as minor products. See Ukiya, et al., J. Agric. Food Chem. 50, 6710-6715 (2002). Glycoside intermediates exist in both 11-hydroxy and 11-oxo series, and gradually change from mogroside I to mogroside V as fruits ripen, which indicates that the triterpene core is fully oxidized by P450 enzymes before the subsequent glycosylations. However, the enzymes responsible for producing mogrosides have not been identified.